This invention relates to a roll setting device for rolling mills for metal bars or the like.
In rolling mills for metal bars or rods, the rolls must notably be carefully set before rolling, this operation comprising centering the rolls and setting the pass between the rolls and the clearance of the bearings. The operation results in long assembly time, as the maximum care must be taken in assembly because even small dissymmetry in the passage section or any displacement in the shape of the section from that theoretically determined leads to considerable difficulties, the most important of which is torsion in the bar or rod being produced.
This torsion leads to an increase in the power required in the individual rolling units and to a product comprising internal stresses and non-uniformity of structure, which make the product one of inferior quality unsuitable for subsequent drawing.
The proper operation of the rolling mill requires that certain rigorous geometrical conditions of mutual positioning of the working surfaces of the rolls, between which the pass is defined for the product to be rolled, be satisfied during assembly. These conditions are that the roll axes must be coplanar, the plane common to the roll axes must be perpendicular to the axis of rolling, and the cross-section of the passage must be symmetrical about the point of intersection of the axis of rolling with the plane defined by the roll axes.
Two operations are required during assembly to make the passage cross-section symmetrical, i.e. centering the rolls and adjusting the pass. In practice, these operations involve setting the rolls to obtain tangency between the rolling surfaces and a circle with its centre at the axis of rolling and of determined diameter, this diameter strictly depending on the position which the rolling unit concerned occupies in the rolling sequence. In this respect, to avoid traction or compression of the metal being rolled, the ratio of the areas of two successive passes must exactly correspond to that determined at the design stage, and as this ratio is the result of much theoretical or practical study, strict setting of the pass of each rolling unit is essential for proper operation.
The said centering of the rolls and adjusting of the pass are attained in practice by moving the rolls in two directions in the common plane of the axes which must be perpendicular to the axis of rolling, one of these directions coinciding with the roll axis, and which is used for centering, and the other being perpendicular to the roll axis, and which is used for adjusting the pass.
These adjusting operations become more complicated and laborious in terms of assembly times when the rolling unit comprises three rolls disposed at 120.degree..
At present these units are constructed in such a manner that the said setting is done by placing shims between roll support parts and the frame block structure. In particular, units have been made in which two of the roll support shafts, complete with bearings and shim, are mounted in two housings extractable from the frame block, the shims being placed between the support surfaces of the frame block and the housing, and between the bearings and the housing, respectively. Setting is carried out by varying these shims as required, those between the support surfaces of the frame block and housing being varied for adjusting the pass and those between the bearings and housing for adjusting the centering and the clearance of the bearings.
This system however presents considerable disadvantages in terms of the time necessary for setting up the rolling unit. This setting up involves the following successive operations: initial assembly with approximate shims, measurement of the centering and pass to determine the correct size of the shims on the basis of these measurements, dismounting the unit including the housings, replacing the shims with those determined by the measurements made, and further reassembly which may be subject to further satisfactory checking before the rolls are finally set.
It is evident that a succession of operations of this type, which have to be carried out for each successive rolling unit of a rolling mill and comprising a different calculation each time of the required shims, lead to an extremely long setting-up and consequently unproductive time for the rolling mill.
The fundamental object of the present invention is to provide a device for setting the rolls of rolling mills for metal bars or the like, with which it is possible to make roll setting more immediate and easy, and at the same time improving setting accuracy with respect to the accuracy obtainable by known devices.
A further object of the present invention is to provide a device so constructed that the rigidity of that part of the structure most directly stressed mechanically is increased, to the advantage of the length of time for which the settings may be maintained.